This invention relates to a novel microorganism and to the novel compositions of matter produced therefrom. More particularly, this invention relates to a novel antibiotic AT 2433 complex produced by fermentation under controlled conditions using a biologically pure culture of a new microorganism Actinomadura melliaura sp. nov., a species of the genus Actinomadura. This invention also relates to the use of antibiotic complex AT 2433 and the four components thereof as antibacterial agents and to their use as antitumor agents.